Such a cross-member has the advantage of locating the metal structural element of the vehicle and the air flow ducts concentrically, taking advantage of the tubular nature of the metal structural element. That leads to a saving in volume compared with a more conventional structure in which the structural element is disposed substantially parallel to, but not concentrically with the air flow ducts.
For reasons of heat losses due to the good thermal conductivity characteristics of steel, it is necessary to ensure that the air being transported does not come into direct contact with the tubular metal structural element, since otherwise the heating ventilation and air conditioning (HVAC) unit on board the vehicle would need to be overdimensioned in order to accommodate said losses. It is therefore known to make the air flow duct out of a plastics material enabling the air it transports to be insulated from the steel of the cross-member.
U.S. Pat. No. 6,422,633 or DE 10 046 120 disclose motor vehicle dashboard cross-members each comprising a tubular metal structural element assembled to the front pillars of the motor vehicle and at least one air flow duct of plastics material for transporting air to the passenger compartment of the motor vehicle, which plastics duct is disposed at least in part inside the metal structural element. The fabrication methods envisaged in those documents rely on hybrid technologies in which the metal structure has elements of plastics material overmolded thereon to constitute in particular the air flow ducts. The plastics material elements also have a reinforcement function and contribute in part to the structural function of the cross-member. Such methods have the advantage of reducing the number of process steps and/or the number of intermediate products in the production cycle. However, that saving is achieved at the expense of a stage of developing the air flow cross-member and its associated tooling that is more complex, and thus leads to costs of fabricating and using the associated tools that are much greater than those conventionally associated with making a cross-member having parallel air flow ducts.